Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LUBRICANT FOR POWDER METALLURGICAL COMPOSITIONS
The present invention relates to a powder metallur-
gical composition. Specifically, the invention relates to
a powder metal composition comprising a new particulate
composite lubricant. The invention further relates to the
new particulate composite lubricant as well as a method
of preparing this lubricant.
In the Powder Metallurgy industry (PM industry) pow-
dered metals, most often iron-based, are used for produc-
tion of components. The production process involves com-
paction of a powder metal blend in a die to form a green
compact, ejecting the compact from the die and sintering
the green compact at temperatures and under such condi-
tions that a sintered compact having sufficient strength
is produced. By using the PM production route costly ma-
chining and material losses can be avoided compared to
conventional machining of components from solid metals as
net shape or nearly net shape components can be produced.
The PM production route is most suitable for the produc-
tion of small and fairly intricate parts such as gears.
In order to facilitate the production of PM parts
lubricants may be added to the iron-based powder before
compaction. By using lubricants the internal frictions
between the individual metal particles during the compac-
tion step are reduced. Another reason for adding lubri-
cant is that the ejection force and the total energy
needed in order to eject the green part from the die af-
ter compaction are reduced. Insufficient lubrication will
result in wear and scuffing at the die during the ejec-
tion of the green compact.
The problem with insufficient lubrication can be
solved mainly in two ways, either by increasing the
amount of lubricant or by selecting more efficient lubri-
cants. By increasing the amount of lubricant, an unde-
sired side effect is however encountered in that the gain
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in density through better lubrication is reversed by the
increased amount of the lubricants.
A better choice would then be to select more
efficient lubricants. This is however a problem as
compounds having good lubricity in PM context tends to
agglomerate during storage or contributes to agglomerate
formation in the powder metallurgical composition, a
consequence of which is that the subsequently compacted
and sintered component may include comparatively large
pores which have a detrimental effect of the static and
dynamic mechanical properties of the component. Another
problem is that lubricants having good lubrication
properties often have negative effects on the so-called
powder properties, such as flow rate and apparent density
(AD). The flow rate is important because of its impact on
the die filling which in turn is important for the
production rate of the PM parts. A high AD is important
in order to enable shorter filling depths and even AD is
important in order to avoid variations in dimensions and
weight of the finished components. It is thus desirable
to obtain a new lubricant for powder metal compositions
that overcomes or reduces the above mentioned problems.
Objects of the invention
An object of the present invention is therefore to
provide a lubricant having good lubrication properties
but no or reduced tendency to agglomerate.
Another object of the present invention is to
provide a lubricant having good lubrication properties
and yet imparting flow or improved flow properties when
it is used in an iron or iron-based powder composition.
Another object is to provide a new iron or iron-
based powder composition which includes the new lubricant
and which has good flow properties and a high and even
apparent density.
Still another object is to provide a process for
producing a lubricant.
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Summary of the invention
According to the invention it has now unexpectedly
been found that the above objects can be met by an iron-
based powder metallurgical composition comprising an iron
or iron-based powder and a new particulate composite
lubricant, said composite lubricant comprising particles
having a core comprising a solid organic lubricant having
fine carbon particles adhered thereon.
The invention also concerns the particulate
composite lubricant per se as well as the preparation
thereof.
Detailed description of the invention
The type of solid organic lubricant of the composite
lubricant according to the invention is not critical, but
due to the disadvantages with metal-organic lubricants,
the organic lubricant should preferably not include metal
constituents. Thus the organic lubricant may be selected
from a wide variety of organic substances having good lu-
bricating properties. Examples of such substances are
fatty acids, waxes, polymers, or derivates and mixtures
thereof.
Preferred solid organic lubricants are fatty acids
selected from the group consisting of palmitic acid
stearic acid, behenic acid and; fatty acid monoamides se-
lected from the group consisting of palmitamide, steara-
mide, behenamide, oleamide and erucamide, fatty acid bis-
amides, such as ethylene bisstearamide (EBS), ethylene
bisoleamide (EBO), polyethylene, polyethylene wax;
secondary fatty acid amides selected from the group con-
sisting of erucyl stearamide, oleyl palmitamide, stearyl
erucamide, stearyl oleamide, stearyl stearamide, oleyl
stearamide.
Especially preferred solid organic lubricants are
stearamide, erucamide, stearyl oleamide, erucyl
stearamide, stearyl erucamide, EBO, EBS, and EBS in
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combination with oleamide, erucamide, stearyl oleamide
stearyl erucamide or erucyl stearamide. Presently
available results indicate that powder metal compositions
comprising these composite lubricants according to the
invention are distinguished by especially high apparent
densities and/or flow rates. Additionally these
lubricants are known for their excellent lubricating
properties.
The average particle size of the organic core parti-
cles may be 0.5-100 m, preferably 1-50 m and most pref-
erably 5-40 m. Furthermore it is preferred that the par-
ticle size of the core is at least five times the
particle size of the carbon particles and it is preferred
that the fine carbon particles form a coating on the core
surface.
In this context the term "fine carbon particles" is
intended to mean crystalline, semi-crystalline or
amorphous carbon particles. The fine carbon particles may
originate from natural or synthetic graphite, carbon
black, activated carbon, coal and anthracite etc and may
also be a mixture of two or more of these. The fine
carbon particles adhered onto the surface of the solid
organic lubricant core may preferably be selected from
the group consisting of carbon black and natural or
synthetic graphite, having an average particle size of
less than 10 m and larger than 5 nm.
The primary particle size of the carbon black may be
less than 200 nm, preferably less than 100 nm, and most
preferably less than 50 nm and larger than 5 nm. The spe-
cific surface area may be between 20 and 1000 m2/g as
measured by the BET-method. Carbon black may be obtained
from a supplier such as Degussa AG, Germany. The content
of carbon black in the composite lubricant may be 0.1-25
% by weight, preferably 0.2-6 o by weight and most pre-
ferably 0.5-4 % by weight.
The average particle size of the graphite may be
less than 10 m and larger than 500 nm. The content of
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graphite in the composite lubricant may be 0.1-25 % by
weight, preferably 0.5-10 % by weight and most preferably
1-7 % by weight. Graphite may be obtained from a supplier
such as Graphit Kropfmuhl AG, Germany or a synthetic
5 graphite with an ultra-high surface area from Asbury
Carbons, USA.
The content of the composite lubricant in the powder
metal composition may be 0.05-2 % by weight.
The particulate composite lubricant according to the
invention may be prepared by ordinary particle coating
technique involving mixing an organic particulate lubri-
cating material and fine carbon particles. The method may
further comprise a heating step. The temperature for the
heat-treatment may be below the melting point of the
solid particulate organic lubricant.
The particulate solid organic lubricant may be thor-
oughly mixed with the fine carbon particles in a mixer.
The mixer may be a high-speed mixer. The mixture may be
heated during mixing at a temperature and during a time
period sufficient to let the fine carbon particles adhere
to the surface of the particulate organic lubricating ma-
terial during a subsequently followed optional cooling
step.
The iron-based powder may be a pre-alloyed iron-
based powder or an iron-based powder having the alloying
elements diffusion-bonded to the iron-particles. The
iron-based powder may also be a mixture of essentially
pure iron powder or pre-alloyed iron-based powder and al-
loying elements selected from the group consisting of Ni,
Cu, Cr, Mo, Mn, P, Si, V, Nb, Ti, W and graphite. Carbon
in the form of graphite is an alloying element used to a
large extent in order to give sufficient mechanical prop-
erties to the finished sintered components. By adding
carbon as an individual constituent to the iron-based
powder composition the dissolved carbon content of the
iron-based powder may be kept low enhancing improved com-
pressibility. The iron-based powder may be an atomized
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powder, such as a water atomized powder, or a sponge iron
powder. The particle size of the iron-based powder is se-
lected depending on the final use of the material. The
particles of the iron or iron-based powder may have a
weight average particle size of up to about 500 lam, more
preferably the particles may have a weight average
particle size in the range of 25-150 pm, and most pref-
erably 40-100 pm.
The powder metal composition may further comprise
one or more additives selected from the group consisting
of binders, processing aids, hard phases, machinability
enhancing agents if there is a need of machining of the
sintered component, and solid lubricants conventionally
used in PM-industry such as EBS, zinc-stearate and
Kenolubeo available from Hoganas AB. The concentration of
the powdered composite lubricant according to the inven-
tion plus optional solid lubricants may be in the range
of 0.05 to 2 % of a powder metal composition.
The new iron or iron-based powder composition may be
compacted and optionally sintered by conventional PM
techniques.
The following examples serve to illustrate the in-
vention but the scope of the invention should not be lim-
ited thereto.
Examples
Materials
The following materials were used.
(1) As iron-based water atomized powder (ASC100.29,
available from Hoganas AB, Sweden) was used.
(2) As lubricating core materials the following
substances were used; ethylene bis-stearamide (EBS)
available as LicowaxTM from Clariant (Germany),
stearamide, erucamide, oleyl palmitamide, stearyl
oleylamide, erucyl stearamide, stearyl erucamide,
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ethylene bis-oleamide (EBO) and polyethylene waxes.
The average particle sizes of the lubricants can be
seen in Table 2.
(3) Graphite UF-4 (from Graphit Kropfmuhl AG,
Germany) was used as added graphite in the iron-
based powder composition.
(4) Coating particles were Graphite UF-1 (UF1)
(from Graphit Kropfmuhl AG, Germany) and Graphite
4827 (4827) (from Asbury Carbons, USA) having an
average particle size of 2 m and 1.7 m
respectively, and Carbon black (CB) (from Degussa
AG, Germany) having a primary particle size of 30
nm.
The iron-based powder compositions consisted of
ASC100.29 mixed with 0.5 % by weight of graphite and 0.8
o by weight of composite lubricant.
Different composite lubricants were prepared by mix-
ing core material according to Table 1 and 2 with fine
carbon particles at different concentrations in a high-
speed mixer from Hosokawa. Carbon black was added at the
concentrations of 0.75, 1.5, 3 and 4 % by weight,
respectively. Graphite was added at the concentrations of
1.5, 3, 5 and 6% by weight, respectively to the composite
lubricants. The process parameters for the mixing
process, such as temperature of the powder in the mixer
and the mixing times for each composite can be seen in
Table 2. The rotor speed in the mixer was 1000 rpm and
the amount of lubricant core material was 500 g.
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Table 1. Lubricating substances used
as core materials.
Mark Common name
ES Erucyl stearamide
OP Oleyl palmitamide
S Stearamide
0 Oleamide
E Erucamide
EBS Ethylene bis-stearamide
PW655 Polyethylene wax
PW1000 Polyethylene wax
SE Stearyl erucamide
EBO Ethylene bis-oleamide
SO Stearyl oleamide
Table 2. Process parameters
Average particle Temp. of powder in
ark size X50 ( m) the mixer ( C) Mixing time (min)
S-1 5.2 50 C 25
S-2 5.8 50 C 25
S-3 15.4 50 C 25
S-4 16.5 50 C 45
S-5 17.8 50 C 25
S-6 21.5 50 C 25
S-7 4.0 83 C 60
ES-1 24.0 25 C 25
ES-2 29.5 25 C 25
E 20.3 25 C 45
OP 16.0 25 C 45
EBS 8.5 75 C 55
EBS/O 25.6 40 C 20
PW655 10.0 25 C 45
PW1000 10.0 40 C 45
SE 27.4 25 C 45
SO 35.4 25 C 45
IEBS/SE 29.0 25 C 45
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Table 2 continued
EBS/SO 29.2 25 C 45
EBS/ES 20.4 25 C 45
EBS/E 26.0 25 C 15
S/E 24.3 25 C 45
EBO 16.0 50 C 10
Different iron-based powder compositions (mix no
1-63) of 25 kg each were prepared by mixing the obtained
composite lubricant or a conventional particulate lubri-
cant (used as reference) with graphite and ASC100.29 in a
50 kg Nauta mixer The solid organic lubricant particles
in mixes no 36-38 and 50-61 were melted, subsequently
solidified and micronised before used as a core material
for preparing the composite lubricants or before added to
the reference mixes. Apparent density (AD) and Hall flow
(flow), were measured, according to ISO 4490 and IS03923-
1, respectively, on the obtained iron-based powder
compositions 24 hours after the mixing. Table 3 shows the
results of the measurements.
As can be seen from table 3, the flow rate of the
iron-based powder compositions is improved and higher ap-
parent densities may be obtained when using the different
composite lubricants according to the invention as lubri-
cants compared with the use of a conventional lubricant.
In fact, when a PM composition containing a conventional
lubricant has no flow the PM composition containing the
inventive composite lubricant provides flow. Especially
high apparent densities and/or flow rates were obtained
for powder metal compositions containing composite lubri-
cants according to the invention containing stearamide,
erucamide, erucyl stearamide, stearyl erucamide, EBO, EBS
and EBS in combination with oleamide or stearyl
erucamide.
In order to measure the tendency of the composite
lubricants and the conventional lubricants to form ag-
glomerates the lubricants were sieved on a standard 315
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m sieve after storage of at least one week. The amount
of the retained material was measured.
Table 4 shows that the tendency of forming agglomer-
ates decreases when the organic lubricating core material
5 is covered by fine carbon particles resulting in a com-
posite lubricant according to the invention.
The same type of measurements as shown in table 4
was repeated with certain iron-based powder compositions
in order to evaluate the tendency of forming agglomerates
10 in an iron-based powder composition containing conven-
tional lubricants and composite lubricants according to
the invention, respectively.
Table 5 shows that the tendency of forming
agglomerates is less pronounced in iron-based powder
compositions containing the composite lubricant according
to the invention compared with compositions comprising a
conventional lubricant.
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Table 3 , Flow rate and apparent density (AD) of composi-
tions 1-63
Mix Conven- Core of Type of Percentage Flow AD
no tional lubri- Carbon of carbon (seconds/ (g/cm3)
lubricant cating particles particles 50g)
used as composite adhered onto in relation
reference lubricating to total
core amount of
lubricating
composite
M
1 S-1 No flow 2.97
2 S-i UF1 3.0 No=flow 2.99
3 S-1 CB 1.5 34.5 2.85
4 S-1 CB 3.0 30.4 2.92
S-2 No flow 2.98
6 S-2 UF1 3.0 No flow 2.99
7 S-2 CB 3.0 32.9 2.91
8 S-3 No flow 3.05
9 S-3 UF1 3.0 29.5 3.17
S-4 No flow 3.12
11 S-4 UF1 3.0 28.3 3.18
12 S-4 CB 0.75 27.1 3.21
13 S-4 CB 1.5 27.2 3.17
14 S-5 30.6 3.05
S-5 CB 0.75 28.5 3.13
16 S-5 CB 1.5 27.3 3.13
17 S-5 4827 5.0 29.3 3.17
is S-6 31.5 3.06
19 S-6 UF1 3.0 27.7 3.20
S-6 CB 0.75 26.9 3.21
21 S-7 28.2 3.17
22 S-7 UF1 3.0 26.1 3.19
23 S-7 CB 3.0 26.0 3.11
24 ES-1 No flow 3.10
ES-1 CB 1.5 33.1 3.19
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Table 3 Continued
Mix Conven- Core of Type of Percentage Flow AD
no tional lubri- Carbon of carbon (seconds/ (g/cm3)
lubricant cating particles particles 50g)
used as composite adhered onto in relation
reference lubricating to total
core amount of
lubricating
composite
(%)
26 ES-2 No flow 3.13
27 ES-2 CB 1.5 31.3 3.15
28 ES-2 4827 1.5 29.7 3.18
29 E No flow 3.03
30 E CB 1.5 30.3 2.97
31 E CB 3.0 28.8 3.01
32 OP No flow 2.92
33 OP CB 1.5 34.3 2.94
34 EBS 33.5 3.01
35 EBS CB 1.5 30.8 3.00
36 EBS/O 31.0 3.03
37 EBS/0 UF1 3.0 30.4 3.10
38 EBS/O CB 3.0 28.4 3.09
39 PW655 No flow 2.76
40 PW655 CB 1.5 32.1 2.82
41 PW1000 No flow 2.78
42 PW1000 CB 1.5 32.5 2.85
43 Zn-stearat 35.4 3.18
44 SE No flow 2.96
45 SE CB 3.0 29.9 3.11
46 SE UF1 6.0 31.2 3.08
47 SE 4827 5.0 30.4 3.10
48 SO No flow 2.95
49 SO CB 1.5 30.9 2.98
50 EBS/SE No flow 2.98
51 EBS/SE CB 1.5 29.6 3.17
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Table 3 continued
52 EBS/SO No flow 2.95
53 EBS/SO CB 1.5 30.9 3.03
54 EBS/ES No flow 3.00
55 EBS/ES CB 1.5 33.4 2.99
56 EBS/E No flow 2.96
57 EBS/E CB 1.5 30.0 3.03
58 S/E No flow 3.00
59 S/E CB 4.0 29.1 3.16
60 S/E UF1 6.0 28.4 3.17
61 S/E 4827 5.0 28.2 3.18
62 EBO No flow 2.95
63 EBO CB 3.0 34.0 3.04
Table 4 Tendency of forming agglomerates for conven-
tional lubricants and lubricating composites according to
the invention
Conven- Core material Type of Percentage Tendency of
tional of lubricating Carbon of carbon forming
lubricant composite particles particles in agglomerates
adhered onto relation to
lubricating total amount of
core lubric
material composite (%)
S-1 Aggl
S-1 CB 1.5 Less aggl
S-i CB 3.0 Less aggl
S-2 Aggl
S-2 CB 3.0 Less aggl
S-4 Aggl
S-4 UF1 3.0 No aggl
S-4 CB 0.75 No aggl
S-4 CB 1.5 No aggl
S-5 Aggl
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Table 4 continued
S-5 CB 0.75 No aggl
S-5 CB 1.5 No aggl
S-5 4827 5,0 No aggl
S-7 Aggl
S-7 UF1 3.0 No aggl
S-7 CB 0.75 No aggl
ES-2 Aggl
ES-2 CB 1.5 No aggl
ES-2 4827 1.5 No aggl
E Aggl
E CB 1.5 Less aggl
OP Aggl
OP CB 1.5 No aggl
EBS No aggl
EBS CB 1.5 No aggl
EBS/O No aggl
EBS/O UF1 3.0 No aggl
SE Aggl
SE CB 1.5 No aggl
SE UF1 6.0 No aggl
SE 4827 5.0 No aggl
60 Aggl
SO CB 1.5 No aggl
EBS/SE Aggl
EBS/SE CB 1.5 No aggl
EBS/SO Aggl
EBS/SO CB 1.5 No aggl
EBS/ES Aggl
EBS/ES CB 1.5 No aggl
EBS/E Aggl
EBS/E CB 1.5 No aggl
S/E Aggl
S/E CB 4.0 No aggl
S/E UF1 6.0 No aggl
S/E 4827 5.0 No aggl
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Table 4 continued
EBO Aggl
EBO CB 3.0 No aggl
Table 5 Tendency of forming agglomerates in iron-based
powder compositions containing conventional lubricants
5 and the composite lubricant according to the invention
Mix Conven- Core Type of Percentage Tendency of
no tional material carbon of carbon forming
lubricant of particles particles in agglomerates
composite adhered onto relation to
lubricant lubricating total amount
core of
material lubricating
composite
(%)
1 S-1 Aggl
3 S-1 CB 1.5 No aggl
4 S-1 CB 3.0 No aggl
5 S-2 Aggl
7 S-2 CB 3.0 No aggl
24 ES-1 Aggl
ES-i CB 1.5 No aggl
29 E Aggl
E CB 1.5 Less aggl
31 E CB 3 No aggl
32 OP Aggl
33 OP CB 1.5 No aggl
34 EBS No aggl
EBS CE 1.5 No aggl
39 PW655 Aggl
PW655 CB 1.5 No aggl
41 PW1.ooo Agg1
42 PW1000 CB 1.5 No aggl
43 Zn-stearate No aggl
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Table 5 continued
44 SE Aggl
45 SE CB 1.5 No aggl
46 SE UF1 6.0 No aggl
47 SE 4827 5.0 No aggl
48 SO Aggl
49 SO CB 1.5 No aggl
50 EBS/SE Aggl
51 EBS/SE CB 1.5 No aggl
52 EBS/SO Aggl
53 EBS/SO CB 1.5 No aggl
54 EBS/ES Aggl
55 EBS/ES CB 1.5 No aggl
56 EBS/E Aggl
57 EBS/E CB 1.5 No aggl
58 S/E Aggl
59 S/E CB 4.0 No aggl
60 S/E UF1 6.0 No aggl
61 S/E 4827 5.0 No aggl
62 EBO Aggl
63 EBO CB 3.0 No Aggl
